With reference to FIGS. 6 to 8, a conventional keyswitch comprises at least a key cap 6 and a hollow plunger 7 connected with the key cap 6. The key top 61 of the key cap 6 has a cross-shaped pole 62 extending from its bottom surface that engages two pairs of ribs 71 within the hollow plunger 7. The cross-shaped pole 62 should be tightly fit with the pairs of ribs 71 to facilitate the key pressing operation. However, the key cap 6 is made with a predetermined rigid material, and the hollow plunger 7 must be made with flexible material to allow tight fitting with the key cap 6. Material and manufacture costs are thereby increased. Moreover, the top portion of the plunger 7 is liable to crack when being assembled with the rigid key cap 6.
The plunger 7 has two bevels 72 formed on both sides thereof. The bevels 72 engage two lengthwise slits 83 formed in the inner sleeve 82 housed by an outer sleeve 81 of a plunger stage 8. The plunger 7 has two annular shaped portions 73 formed thereon to receive the bottoms of outer and inner sleeves 81 and 82 such that the space within the outer sleeve 81 is sealed. This kind of keyboard keyswitch is employed in cash registers and is formed with a bump 74 on the bottom of the plunger 7 to contact a switch sheet. However, this keyboard is of a two-piece design, and the structure thereof is complicated. Moreover, an elastic ring 9 is arranged on a step portion 84 on top of the outer sleeve 81 to provide restoring force and prevent the entry of dust and droplets. However, the structure is not satisfactory and requires improvement.
It is the object of the present invention to provide a dustproof and droplet-proof keyswitch wherein a key cap and a plunger are inserted into a stage on a base plate, and an elastic member between the stage and the key cap provides a seal for the keyswitch against dust and droplet entry. Therefore, the keyswitch can be used under severe conditions such as in a dusty environment or when the keyboard has spilled upon it a liquid such as tea or coffee.
To achieve the above objects, a dustproof and droplet-proof keyswitch comprises a base plate with at least one stage formed thereon, each having a step portion on top of the stage; an elastic member arranged on the step portion; a key cap mounted on the elastic member and having a plunger inserting into the stage. The plunger has an elastic plate clamped between a pair of grooves and having a hook on a lower end thereof; the hook having a beveled lower end thereof latched with the stage when the key cap is released. The stage has at least one projecting rib on an inner side thereof corresponding to at least one notch on the plunger to provide a clamping effect.